add context to parser, that would hold local variable info, filename, and line number.  mrbc_context argument has been added to mrb_parse_xxx() functions.  Normally, you just to need to add NULL (or 0) to the last argument of the above functions.

modify compiler API; replace mrb_compie_xxx with mrb_load_xxx() that combines compilatoin and execution

Initialize mt of module with khash.

Fix str_replace in string.c

Free iv of MRB_TT_DATA instance.

 - Increment refcnt of shared string.
 - Free buffer before replacing.
 - Clear MRB_STR_SHARED after decref is called.
 - Fix target of aux.capa.

Make strucdata optional if ENABLE_STRUCT is activated

Sprintf NotImplementedError

Supress "warning: array subscript has type ‘char’"

Use sizeof to get char array sizes.

Fix str_format_len.